When a driver turns a steering wheel of a vehicle travelling or stopped in one direction, the vehicle wheels, which are in contact with a road surface, are turned in the same direction. A great amount of load is applied to the vehicle wheels turned by the steering wheel due to friction against the road surface.
For this reason, a conventional steering wheel system is equipped with an electric hydraulic power steering (EHPS) system. This EHPS system is adapted to sense amounts of torque generated from the steering wheel and the vehicle wheels when the driver turns the steering wheel, and allow a powering means to generate repulsive force corresponding to a deviation between the torque amounts so as to turn the vehicle wheels, thereby facilitating manipulation of the steering wheel.
The conventional EHPS system, however, has drawbacks. In particular, the electric hydraulic pump of the EHPS system, which feeds hydraulic pressure to a drive unit coupled with the steering wheel, is driven even when the steering wheel is not manipulated, resulting in unnecessary power consumption. Further, the current consumed when the steering wheel is not manipulated acts as an electric load to the vehicle, lowering fuel efficiency.
The above information disclosed in this Background Art section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.